Molecular Mechanisms of Oxidative Stress Relief by CAPE in ARPE-19 Cells

Caffeic acid phenylethyl ester (CAPE) is an antioxidative agent originally derived from propolis. Oxidative stress is a significant pathogenic factor in most retinal diseases. Our previous study revealed that CAPE suppresses mitochondrial ROS production in ARPE-19 cells by regulating UCP2. The present study explores the ability of CAPE to provide longer-term protection to RPE cells and the underlying signal pathways involved. ARPE-19 cells were given CAPE pretreatment followed by t-BHP stimulation. We used in situ live cell staining with CellROX and MitoSOX to measure ROS accumulation; Annexin V-FITC/PI assay to evaluate cell apoptosis; ZO-1 immunostaining to observe tight junction integrity in the cells; RNA-seq to analyze changes in gene expression; q-PCR to validate the RNA-seq data; and Western Blot to examine MAPK signal pathway activation. CAPE significantly reduced both cellular and mitochondria ROS overproduction, restored the loss of ZO-1 expression, and inhibited apoptosis induced by t-BHP stimulation. We also demonstrated that CAPE reverses the overexpression of immediate early genes (IEGs) and activation of the p38-MAPK/CREB signal pathway. Either genetic or chemical deletion of UCP2 largely abolished the protective effects of CAPE. CAPE restrained ROS generation and preserved the tight junction structure of ARPE-19 cells against oxidative stress-induced apoptosis. These effects were mediated via UCP2 regulation of p38/MAPK-CREB-IEGs pathway.

Epigenetics and Degenerative Retinal Diseases: Prospects for New Therapeutic Approaches

ABSTRACT

There is growing evidence that retinal degenerative diseases are accompanied by epigenetic changes in both deoxyribonucleic acid methylation and histone modification. Even in the monogenic disease retinitis pigmentosa, there is a cascade of changes in gene expression that correlate with epigenetic changes, suggesting that many of the symptoms, and degenerative changes, may be a result of epigenetic changes downstream from the genetic mutation. This is supported by data from studies of diabetic retinopathy and macular degeneration, 2 diseases where it has been difficult to define a single causative change. Initial studies with modifiers of deoxyribonucleic acid methylation suggest that they can provide therapeutic benefit. A number of drugs are available to inhibit specific epigenetic histone modifier enzymes, and these offer the possibility of new therapeutic approaches to retinal disease. Systemic treatment with inhibitors of histone demethylases and histone deacetylases have arrested rod degeneration in rodent models of retinitis pigmentosa. Some evidence has suggested that similar treatments may provide benefits for patients with diabetic retinopathy. Because differentiation of retinal stem cells is regulated in part by epigenetic mechanisms, it may also be possible to direct stem cell differentiation pathways through the use of selective epigenetic modifiers. This is predicted to provide a valuable avenue to accelerate the introduction of regenerative approaches to retinal disease. Epigenetic modifiers are poised to become a powerful new approach to treat retinal degenerative diseases.

Uncoupling Proteins as Therapeutic Targets for Neurodegenerative Diseases

Most of the major retinal degenerative diseases are associated with significant levels of oxidative stress. One of the major sources contributing to the overall level of stress is the reactive oxygen species (ROS) generated by mitochondria. The driving force for ROS production is the proton gradient across the inner mitochondrial membrane. This gradient can be modulated by members of the uncoupling protein family, particularly the widely expressed UCP2. The overexpression and knockout studies of UCP2 in mice have established the ability of this protein to provide neuroprotection in a number of animal models of neurological disease, including retinal diseases. The expression and activity of UCP2 are controlled at the transcriptional, translational and post-translational levels, making it an ideal candidate for therapeutic intervention. In addition to regulation by a number of growth factors, including the neuroprotective factors LIF and PEDF, small molecule activators of UCP2 have been found to reduce mitochondrial ROS production and protect against cell death both in culture and animal models of retinal degeneration. Such studies point to the development of new therapeutics to combat a range of blinding retinal degenerative diseases and possibly other diseases in which oxidative stress plays a key role.

Novel Regulators of Retina Neovascularization: A Proteomics Approach

The purpose of this study was to identify proteins that regulate vascular remodeling in an ROP mouse model. Pups were subjected to fluctuating oxygen levels and retinas sampled during vessel regression (PN12) or neovascularization (PN17) for comparative SWATH-MS proteomics using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We developed a human retinal endothelial cell (HREC) ROP correlate to validate the expression of retina neovascular-specific markers. A total of 5191 proteins were identified in OIR retinas with 498 significantly regulated in elevated oxygen and 345 after a return to normoxia. A total of 122 proteins were uniquely regulated during vessel regression and 69 during neovascularization (FC ≥ 1.5; p ≤ 0.05), with several validated by western blot analyses. Expressions of 56/69 neovascular-specific proteins were confirmed in hypoxic HRECs with 23 regulated in the same direction as OIR neovascular retinas. These proteins control angiogenesis-related processes including matrix remodeling, cell migration, adhesion, and proliferation. RNAi and transfection overexpression studies confirmed that VASP and ECH1, showing the highest levels in hypoxic HRECs, promoted human umbilical vein (HUVEC) and HREC cell proliferation, while SNX1 and CD109, showing the lowest levels, inhibited their proliferation. These proteins are potential biomarkers and exploitable intervention tools for vascular-related disorders. The proteomics data set generated has been deposited to the ProteomeXchange/iProX Consortium with the Identifier:PXD029208.

Neuroprotection of retinal cells by Caffeic Acid Phenylethyl Ester（CAPE) is mediated by mitochondrial uncoupling protein UCP2

Oxidative stress due to mitochondrial produced reactive oxygen species is a major cause of damage seen in many retinal degenerative diseases. Caffeic acid phenylethyl ester （CAPE） is protective agent in multiple tissues and is reported to have anti-oxidant properties. Systemically applied CAPE protected retinal ganglion cells from ischemic injury induced by increased intraocular pressure. CAPE provided complete protection for ARPE19 retinal pigment epithelial cells against tert-butyl hydrogen peroxide and reduced both basal and LPS-stimulated ROS production. The major effect of CAPE was mediated by the mitochondrial uncoupling protein UCP2 since both pharmacological inhibition of UCP2 and siRNA-induced knockdown removed the ability of CAPE to block ROS production. Based on common structural features, CAPE may be acting as a mimetic of the natural UCP2 homeostatic regulator 4-hydroxy-2-nonenal. CAPE may provide a valuable tool to treat oxidative stress-related damage in retinal and other degenerative diseases.

PEDF is an endogenous inhibitor of VEGF-R2 angiogenesis signaling in endothelial cells

Pigment epithelium derived factor (PEDF), an endogenous inhibitor of angiogenesis, targets the growth of aberrant blood vessels in many tissues, including the eye. In this study we show that PEDF prevented early mitogenic signals of vascular endothelial growth factor (VEGF-A) in primate retinal endothelial cells, blocking proliferation, migration and tube formation. PEDF inhibited the phosphorylation and activation of five major downstream VEGF-A signaling partners, namely phosphoinositide-3-OH Kinase (PI3K), AKT, FAK, Src (Y416), and PLC-γ. It did so by binding to the extracellular domain of VEGF-R2, blocking VEGF-A-induced tyrosine phosphorylation (Tyr 951 and Tyr 1175), and inhibiting VEGF-R2 receptor kinase activity. PEDF had no effect on the transcription or translation of VEGF-R2 in cultured HUVECs. PEDF also bound to the extracellular domain of VEGF-R1. We conclude that PEDF blocks the growth of new blood vessels, in part, by reducing VEGF-A activation of its key mitogenic receptor, VEGF-R2, and by preventing its downstream signals in endothelial cells.

PEDF Gene Deletion Disrupts Corneal Innervation and Ocular Surface Function

Purpose

The cornea is richly innervated by the trigeminal ganglion (TG) and its function supported by secretions from the adjacent lacrimal (LG) and meibomian glands (MG). In this study we examined how pigment epithelium–derived factor (PEDF) gene deletion affects the cornea structure and function.

Methods

We used PEDF hemizygous and homozygous knockout mice to study effects of PEDF deficiency on corneal innervation assessed by beta tubulin staining, mRNA expression of trophic factors, and PEDF receptors by adjacent supporting glands, corneal sensitivity measured using a Cochet-Bonnet esthesiometer, and tear production using phenol red cotton thread wetting.

Results

Loss of PEDF was accompanied by reduced corneal innervation and sensitivity, increased corneal surface injury and tear production, thinning of the corneal stroma and loss of stromal cells. PEDF mRNA was expressed in the cornea and its supporting tissues, the TG, LG, and MG. Deletion of one or both PEDF alleles resulted in decreased expression of essential trophic support in the TG, LG, and MG including nerve growth factor, brain-derived neurotrophic growth factor, and GDNF with significantly increased levels of NT-3 in the LG and decreased EGF expression in the cornea. Decreased transcription of the putative PEDF receptors, adipose triglyceride lipase, lipoprotein receptor–related protein 6, laminin receptor, PLXDC1, and PLXDC2 was also evident in the TG, LG and MG with the first three showing increased levels in corneas of the Pedf^+/− and Pedf^−/− mice compared to wildtype controls. Constitutive inactivation of ERK1/2 and Akt was pronounced in the TG and cornea, although their protein levels were dramatically increased in Pedf^−/− mice.

Conclusions

This study highlights an essential role for PEDF in corneal structure and function and confirms the reported rescue of exogenous PEDF treatment in corneal pathologies. The pleiotropic effects of PEDF deletion on multiple trophic factors, receptors and signaling molecules are strong indications that PEDF is a key coordinator of molecular mechanisms that maintain corneal function and could be exploited in therapeutic options for several ocular surface diseases.

Uncoupling proteins in the mitochondrial defense against oxidative stress

Oxidative stress is a major component of most major retinal diseases. Many extrinsic anti-oxidative strategies have been insufficient at counteracting one of the predominant intrinsic sources of reactive oxygen species (ROS), mitochondria. The proton gradient across the inner mitochondrial membrane is a key driving force for mitochondrial ROS production, and this gradient can be modulated by members of the mitochondrial uncoupling protein (UCP) family. Of the UCPs, UCP2 shows a widespread distribution and has been shown to uncouple oxidative phosphorylation, with concomitant decreases in ROS production. Genetic studies using transgenic and knockout mice have documented the ability of increased UCP2 activity to provide neuroprotection in models of a number of diseases, including retinal diseases, indicating that it is a strong candidate for a therapeutic target. Molecular studies have identified the structural mechanism of action of UCP2 and have detailed the ways in which its expression and activity can be controlled at the transcriptional, translational and posttranslational levels. These studies suggest a number of ways in control of UCP2 expression and activity can be used therapeutically for both acute and chronic conditions. The development of such therapeutic approaches will greatly increase the tools available to combat a broad range of serious retinal diseases.

Cell Autonomous Neuroprotection by the Mitochondrial Uncoupling Protein 2 in a Mouse Model of Glaucoma

Glaucoma is a group of disorders associated with retinal ganglion cell (RGC) degeneration and death. There is a clear contribution of mitochondrial dysfunction and oxidative stress toward glaucomatous RGC death. Mitochondrial uncoupling protein 2 (Ucp2) is a well-known regulator of oxidative stress that increases cell survival in acute models of oxidative damage. The impact of Ucp2 on cell survival during sub-acute and chronic neurodegenerative conditions, however, is not yet clear. Herein, we test the hypothesis that increased Ucp2 expression will improve RGC survival in a mouse model of glaucoma. We show that increasing RGC but not glial Ucp2 expression in transgenic animals decreases glaucomatous RGC death, but also that the PPAR-γ agonist rosiglitazone (RSG), an endogenous transcriptional activator of Ucp2, does not significantly alter RGC loss during glaucoma. Together, these data support a model whereby increased Ucp2 expression mediates neuroprotection during a long-term oxidative stressor, but that transcriptional activation alone is insufficient to elicit a neuroprotective effect, motivating further research in to the post-transcriptional regulation of Ucp2.

The 3-Phosphoinositide-Dependent Protein Kinase 1 Inhibits Rod Photoreceptor Development

The transition of rod precursor cells to post-mitotic rod photoreceptors can be promoted by extrinsic factors such as insulin-like growth factor 1 (IGF-1), which regulates phosphatidylinositide concentration, and consequently the 3-phosphoinositide-dependent protein kinase-1 (PDPK-1). PDPK-1 is a 63 kDa cytoplasmic kinase that controls cell proliferation and differentiation. In the mouse retina, PDPK-1 and its phosphorylated derivative p-PDPK-1 (Ser241), showed peak expression during the first postnatal (PN) day with a substantial decline by PN7 and in the adult retina. Though initially widely distributed among cell types, PDPK-1 expression decreased first in the inner retina and later in the outer retina. When PDPK-1 is inhibited in neonatal retinal explants by BX795, there is a robust increase in rod photoreceptor numbers. The increase in rods depended on the activity of PKC, as BX795 had no effect when PKC is inhibited. Inhibition of PDPK-1-dependent kinases, such as P70-S6K, but not others, such as mTORC-1, stimulated rod development. The P70-S6K-dependent increase in rods appears to be correlated with phosphorylation of Thr252 and not at Thr389, a substrate of mTORC-1. This pathway is also inactive while PKC activity is inhibited. We also found that inhibition of the kinase mTORC-2, also stimulated by insulin activity, similarly increased rod formation, and this effect appears to be independent of PKC activity. This may represent a novel intracellular signaling pathway that also stimulates photoreceptor development. Consistent with previous studies, stimulation of STAT3 activity is sufficient to prevent any PDPK-1, P70-S6K, or mTORC2-dependent increase in rods. Together the data indicate that PDPK-1 and other intrinsic kinases downstream of IGF-1 are key regulators of rod photoreceptor formation.

Perineuronal nets labeled by monoclonal antibody VC1.1 ensheath interneurons expressing parvalbumin and calbindin in the rat amygdala

Perineuronal nets (PNNs) are specialized condensations of extracellular matrix that ensheath particular neuronal subpopulations in the brain and spinal cord. PNNs regulate synaptic plasticity, including the encoding of fear memories by the amygdala. The present immunohistochemical investigation studied PNN structure and distribution, as well as the neurochemistry of their ensheathed neurons, in the rat amygdala using monoclonal antibody VC1.1, which recognizes a glucuronic acid 3-sulfate glycan associated with PNNs in the cerebral cortex. VC1.1+ PNNs surrounded the cell bodies and dendrites of a subset of nonpyramidal neurons in cortex-like portions of the amygdala (basolateral amygdalar complex, cortical nuclei, nucleus of the lateral olfactory tract, and amygdalohippocampal region). There was also significant neuropilar VC1.1 immunoreactivity, whose density varied in different amygdalar nuclei. Cell counts in the basolateral nucleus revealed that virtually all neurons ensheathed by VC1.1+ PNNs were parvalbumin-positive (PV+) interneurons, and these VC1.1+/PV+ cells constituted 60% of all PV+ interneurons, including all of the larger PV+ neurons. Approximately 70% of VC1.1+ neurons were calbindin-positive (CB+), and these VC1.1+/CB+ cells constituted about 40% of all CB+ neurons. Colocalization of VC1.1 with Vicia villosa agglutinin (VVA) binding, which stains terminal N-acetylgalactosamines, revealed that VC1.1+ PNNs were largely a subset of VVA+ PNNs. This investigation provides baseline data regarding PNNs in the rat which should be useful for future studies of their function in this species.

Activin Signals through SMAD2/3 to Increase Photoreceptor Precursor Yield during Embryonic Stem Cell Differentiation

In vitro differentiation of mouse embryonic stem cells (ESCs) into retinal fates can be used to study the roles of exogenous factors acting through multiple signaling pathways during retina development. Application of activin A during a specific time frame that corresponds to early embryonic retinogenesis caused increased generation of CRX⁺ photoreceptor precursors and decreased PAX6⁺ retinal progenitor cells (RPCs). Following activin A treatment, SMAD2/3 was activated in RPCs and bound to promoter regions of key RPC and photoreceptor genes. The effect of activin on CRX expression was repressed by pharmacological inhibition of SMAD2/3 phosphorylation. Activin signaling through SMAD2/3 in RPCs regulates expression of transcription factors involved in cell type determination and promotes photoreceptor lineage specification. Our findings can contribute to the production of photoreceptors for cell replacement therapy.

Histone Deacetylase 1 Is Essential for Rod Photoreceptor Differentiation by Regulating Acetylation at Histone H3 Lysine 9 and Histone H4 Lysine 12 in the Mouse Retina

Histone acetylation has a regulatory role in gene expression and is necessary for proper tissue development. To investigate the specific roles of histone deacetylases (HDACs) in rod differentiation in neonatal mouse retinas, we used a pharmacological approach that showed that inhibition of class I but not class IIa HDACs caused the same phenotypic changes seen with broad spectrum HDAC inhibitors, most notably a block in the differentiation of rod photoreceptors. Inhibition of HDAC1 resulted in increase of acetylation of lysine 9 of histone 3 (H3K9) and lysine 12 of histone 4 (H4K12) but not lysine 27 of histone 3 (H3K27) and led to maintained expression of progenitor-specific genes such as Vsx2 and Hes1 with concomitant block of expression of rod-specific genes. ChiP experiments confirmed these changes in the promoters of a group of progenitor genes. Based on our results, we suggest that HDAC1-specific inhibition prevents progenitor cells of the retina from exiting the cell cycle and differentiating. HDAC1 may be an essential epigenetic regulator of the transition from progenitor cells to terminally differentiated photoreceptors.

Uncoupling protein 2 in the glial response to stress: implications for neuroprotection

Reactive oxygen species (ROS) are free radicals thought to mediate the neurotoxic effects of several neurodegenerative disorders. In the central nervous system, ROS can also trigger a phenotypic switch in both astrocytes and microglia that further aggravates neurodegeneration, termed reactive gliosis. Negative regulators of ROS, such as mitochondrial uncoupling protein 2 (UCP2) are neuroprotective factors that decrease neuron loss in models of stroke, epilepsy, and parkinsonism. However, it is unclear whether UCP2 acts purely to prevent ROS production, or also to prevent gliosis. In this review article, we discuss published evidence supporting the hypothesis that UCP2 is a neuroprotective factor both through its direct effects in decreasing mitochondrial ROS and through its effects in astrocytes and microglia. A major effect of UCP2 activation in glia is a change in the spectrum of secreted cytokines towards a more anti-inflammatory spectrum. There are multiple mechanisms that can control the level or activity of UCP2, including a variety of metabolites and microRNAs. Understanding these mechanisms will be key to exploitingthe protective effects of UCP2 in therapies for multiple neurodegenerative conditions.

Mitochondrial Uncoupling Protein 2 (UCP2) Regulates Retinal Ganglion Cell Number and Survival

In the brain, mitochondrial uncoupling protein 2 (UCP2) has emerged as a stress signal associated with neuronal survival. In the retina, UCP2 is expressed primarily by retinal ganglion cells. Here, we investigated the functional relevance of UCP2 in the mouse retina. Increased expression of UCP2 significantly reduced apoptosis during the critical developmental period resulting in elevated numbers of retinal ganglion cells in the adult. Elevated UCP2 levels also protected against excitotoxic cell death induced by intraocular injection of either NMDA or kainic acid. In monolayer cultures of retinal cells, elevated UCP2 levels increased cell survival and rendered the cells independent of the survival-promoting effects of the neurotrophic factors BDNF and CNTF. Taken together, these data implicate UCP2 as an important regulator of retinal neuron survival both during development and in adult animals.

LSD1-Mediated Demethylation of H3K4me2 Is Required for the Transition from Late Progenitor to Differentiated Mouse Rod Photoreceptor

Epigenetic modifiers can work in concert with transcription factors to control the transition of cells from proliferating progenitors into quiescent terminally differentiated cells. This transition involves changes in histone methylation and one of the key regulators of this is the H3K4me2/1 histone demethylase LSD1. Here, we show that the highest expression of LSD1 occurs in postmitotic retinal cells during the peak period of rod photoreceptor differentiation. Pharmacological inhibition of LSD1 in retinal explants cultured from PN1 to PN8 had three major effects. It prevented the normal decrease in expression of genes associated with progenitor function, it blocked rod photoreceptor development, and it increased expression of genes associated with other retinal cell types. The maintained expression of progenitor genes was associated with a maintained level of H3K4me2 over the gene and its promoter. Among the genes whose expression was maintained was Hes1, a repressor known to block rod photoreceptor development. The inhibition of rod photoreceptor gene expression occurred in spite of the normal expression of transcription factors CRX and NRL, and the normal accumulation of H3K4me2 marks over the promoter and gene body. We suggest that LSD1 acts in concert with a series of nuclear receptors to modify chromatin structure and repress progenitor genes as well as to inhibit ectopic patterns of gene expression in the differentiating postmitotic retinal cells.

Regulation of rod photoreceptor differentiation by STAT3 is controlled by a tyrosine phosphatase

Signal pathways that reduce the levels of tyrosine-phosphorylated STAT3 (pSTAT3) allow late retinal progenitors to exit the cell cycle and enter a terminal differentiation pathway into rod photoreceptors. In the mouse retina, we previously identified PKC-β1 and PKC-γ isoforms as essential components of a key signal pathway and IGF-1 as a major extrinsic factor regulating rod formation. In this manuscript, we demonstrate that PKC decreases phosphotyrosine but not phosphoserine on STAT3 in neonatal mouse retinas. Neither IGF-1 nor PMA induced a significant change in the levels of STAT3 or in the levels of the key proteins regulating STAT3 degradation, SOCS3, and PIAS3. Treatment of neonatal mouse retinal explants with sodium orthovanadate inhibited the PKC-mediated reduction in pSTAT3, indicating a role for a phosphatase. Addition of the PTEN inhibitor bpV(phen) to explant cultures treated with IGF-1 or PMA had no effect on the reduction in pSTAT3 levels, but the effect of both IGF-1 and PMA was blocked by a concentration of the inhibitor NSC87877 that is selective for the phosphatases Shp1 and Shp2. Inhibition of Shp1/2 phosphatases was also sufficient to abolish the IGF1-mediated induction of rod photoreceptor differentiation in the retina explant cultures. We conclude that one or both of these phosphatases are key components regulating the formation of rod photoreceptors in mouse retina.

Tetrandrine protects mouse retinal ganglion cells from ischemic injury

This study aimed to determine the protective effects of tetrandrine (Tet) on murine ischemia-injured retinal ganglion cells (RGCs). For this, we used serum deprivation cell model, glutamate and hydrogen peroxide (H₂O₂)-induced RGC-5 cell death models, and staurosporine-differentiated neuron-like RGC-5 in vitro. We also investigated cell survival of purified primary-cultured RGCs treated with Tet. An in vivo retinal ischemia/reperfusion model was used to examine RGC survival after Tet administration 1 day before ischemia. We found that Tet affected RGC-5 survival in a dose- and time-dependent manner. Compared to dimethyl sulfoxide treatment, Tet increased the numbers of RGC-5 cells by 30% at 72 hours. After 48 hours, Tet protected staurosporine-induced RGC-5 cells from serum deprivation-induced cell death and significantly increased the relative number of cells cultured with 1 mM H₂O₂ (P<0.01). Several concentrations of Tet significantly prevented 25-mM-glutamate-induced cell death in a dose-dependent manner. Tet also increased primary RGC survival after 72 and 96 hours. Tet administration (10 μM, 2 μL) 1 day before retinal ischemia showed RGC layer loss (greater survival), which was less than those in groups with phosphate-buffered saline intravitreal injection plus ischemia in the central (P=0.005, n=6), middle (P=0.018, n=6), and peripheral (P=0.017, n=6) parts of the retina. Thus, Tet conferred protective effects on serum deprivation models of staurosporine-differentiated neuron-like RGC-5 cells and primary cultured murine RGCs. Furthermore, Tet showed greater in vivo protective effects on RGCs 1 day after ischemia. Tet and ciliary neurotrophic factor maintained the mitochondrial transmembrane potential (ΔΨm) of primary cultured RGCs and inhibited the expression of activated caspase-3 and bcl-2 in ischemia/reperfusion-insult retinas.

Cell type-specific epigenetic signatures accompany late stages of mouse retina development

We have used ChIP-seq to map the distribution of two important histone H3 modifications, H3K4me2 and H3K27me3, over the whole genome at multiple time points during late mouse retina development. We merged these data with our previous retina developmental expression profiles and show that there are several epigenetic signatures specific for different functional groups of genes. The main conclusion from our study is that epigenetic signatures defined by H3K4me2 and H3K27me3 can distinguish cell-type specific genes from widespread transcripts and may be reflective of cell specificity during retina maturation. Rod photoreceptor-specific genes have a striking signature, a de novo accumulation of H3K4me2 and a complete absence of H3K27me3. We were able to use this signature in an unbiased search of the whole genome and identified essentially all the known rod photoreceptor genes as well as a group of novel genes that have a high probability of being rod photoreceptor specific. Comparison of our genome-wide chromatin signature maps with available data sets for Polymerase-II (Pol-II) and CRX binding sites and DNase1 Hypersensitive Sites (DHS) for retina shows great agreement. Because our approach is not dependent on high levels of gene expression, it provides a new way of identifying cell type-specific genes, particularly genes that may be involved in retinal diseases.

Developmentally regulated linker histone H1c promotes heterochromatin condensation and mediates structural integrity of rod photoreceptors in mouse retina

Mature rod photoreceptor cells contain very small nuclei with tightly condensed heterochromatin. We observed that during mouse rod maturation, the nucleosomal repeat length increases from 190 bp at postnatal day 1 to 206 bp in the adult retina. At the same time, the total level of linker histone H1 increased reaching the ratio of 1.3 molecules of total H1 per nucleosome, mostly via a dramatic increase in H1c. Genetic elimination of the histone H1c gene is functionally compensated by other histone variants. However, retinas in H1c/H1e/H1(0) triple knock-outs have photoreceptors with bigger nuclei, decreased heterochromatin area, and notable morphological changes suggesting that the process of chromatin condensation and rod cell structural integrity are partly impaired. In triple knock-outs, nuclear chromatin exposed several epigenetic histone modification marks masked in the wild type chromatin. Dramatic changes in exposure of a repressive chromatin mark, H3K9me2, indicate that during development linker histone plays a role in establishing the facultative heterochromatin territory and architecture in the nucleus. During retina development, the H1c gene and its promoter acquired epigenetic patterns typical of rod-specific genes. Our data suggest that histone H1c gene expression is developmentally up-regulated to promote facultative heterochromatin in mature rod photoreceptors.

Pigment epithelium-derived factor (PEDF) peptide eye drops reduce inflammation, cell death and vascular leakage in diabetic retinopathy in Ins2(Akita) mice

Inflammation, neurodegeneration and microvascular irregularities are included in the spectrum of defects associated with diabetic retinopathy. Here, we evaluated intraocular deliverability features of two pigment epithelium-derived factor (PEDF) derivatives given as eye drops and their efficacy in modulating diabetes-induced retinal complications. The antiangiogenic PEDF60-77 (P60) and neuroprotective PEDF78-121 (P78) derivatives were applied to Ins2(Akita) mouse eyes once a week for 15 wks at the onset of hyperglycemia. Peptides, labeled with Alexa Fluor 488, were observed penetrating the cornea by 1-4 h and gained access to the ciliary body, retinal pigment epithelium (RPE)-choroid complex, retina microvasculature and vitreous. Peak vitreous levels were 0.2 μg/mL for P60 and 0.9 μg/mL for P78 after 0.5 and 4 h, respectively. Both peptides reduced vascular leakage by ~60% and increased zona occludens 1 (ZO1) and occludin expression in the microvasculature to nondiabetic levels. P60 induced pERK1/2 and P78 promoted pAKT in Muller glia, two signals that were dampened in diabetic conditions. Pharmacologically inhibiting AKT signaling in the retina blocked effects of the peptides on ZO1 and occludin expression. P78 reduced levels of 9/20 cytokines in diabetic vitreous including interferon (IFN)-γ, interleukin (IL)-6, IL-3 and tumor necrosis factor (TNF)-α. P60 lowered levels of 6/20 cytokines but was less effective than P78. Neuroprotective P78 prevented diabetes-induced microglia activation by ~60%, retinal ganglion cell (RGC) death by ~22% and inner plexiform layer thinning by ~13%. In summary, we provide evidence that PEDF bioactive derivatives gained access to the retina by topical delivery and validated their efficacy in reducing diabetic retinopathy complications. Our findings argue for glia regulation of microvascular leakage and an early root cause for RGC degeneration embedded in microglia activation.

MAPK signaling during Müller glial cell development in retina explant cultures

The Müller cell is the only glial cell type generated from the retinal neuroepithelium. This cell type controls normal retina homeostasis and has been suggested to play a neuroprotective role. Recent evidence suggests that mammalian Müller cells can de-differentiate and return to a progenitor or stem cell stage following injury or disease. In vivo exploration of the molecular mechanisms of Müller cell differentiation and proliferation will add essential information to manipulate Müller cell functions. Signal transduction pathways that regulate Müller cell responses and activity are a critical part of their cellular machinery. In this study, we focus on mitogen-activated protein kinase (MAPK) signaling pathway during Müller glial cell differentiation and proliferation. We found that both MAPK and STAT3 signaling pathways are present during Müller glial cell development. Ciliary neurotrophic factor (CNTF)-stimulated Müller glial cell proliferation is associated with early developmental stages. Specific inhibition of MAPK phosphorylation significantly reduced the number of Müller glial cells with or without CNTF stimulation. These results suggested that the MAPK signal transduction pathway is important in the formation of Müller glial cells during retina development.

[Purified mouse retinal ganglion cell culture]

OBJECTIVE

To establish a culture system for purified mouse retinal ganglion cells (RGC) culture in order to lay a foundation for the in vitro study of RGC.

METHODS

It was a experiment study. Eight to twelve C57BL/6 mice on postnatal day 4 to 6 were used. The retinas were dissected and dissociated enzymatically to make a suspension of single cells. The retinal suspension was incubated in rat anti-mouse-macrophage antiserum for 5 minutes and incubated on a 100 mm anti-rat IgG panning plate at room temperature for 30 min twice. The nonadherent cells were removed with the suspension and placed on the Thy-1.2 panning plate at room temperature. After 45 min, plates were washed 6 - 10 times with phosphate-buffered saline and swirled moderately to dislodge nonadherent cells. Trypsin (0.125% solution) dissociation was used to remove adherent cells from the plate. Then cells were spun and resuspended in neurobasal medium containing some neurotrophic factors. The cell suspension was implanted in 24 well culture plates and cultured under 37°C in an incubator with 5% CO(2).

RESULTS

Most of the cells adhered to the plate after 24 hours in culture and showed dendrites at different lengths. The dendrites grew longer with time. Most of the RGC can survive more than two weeks.

CONCLUSION

Monoclonal antibody to the Thy-1.2 antigen can be used to purify the mice RGC.

Mitochondria and the regulation of free radical damage in the eye

Neuronal cell death can be determined by the overall level of reactive oxygen species (ROS) resulting from the combination of extrinsic sources and intrinsic production as a byproduct of oxidative phosphorylation. Key controllers of the intrinsic production of ROS are the mitochondrial uncoupling proteins (UCPs). By allowing a controlled leak of protons across the inner mitochondrial membrane activation of these proteins can decrease ROS and promote cell survival. In both primate models of Parkinson's disease and mouse models of seizures, increased activity of UCP2 significantly increased neuronal cells survival. In the retina UCP2 is expressed in many neurons and glial cells, but was not detected in rod photoreceptors. Retinal ganglion cell survival following excitotoxic damage was much greater in animals overexpressing UCP2. Traditional Chinese medicines, such as an extract of Cistanche tubulosa, may provide benefit by altering mitochondrial metabolism.

Comparison of gene expression during in vivo and in vitro postnatal retina development

Retina explants are widely used as a model of neural development. To define the molecular basis of differences between the development of retina in vivo and in vitro during the early postnatal period, we carried out a series of microarray comparisons using mouse retinas. About 75% of 8,880 expressed genes from retina explants kept the same expression volume and pattern as the retina in vivo. Fewer than 6% of the total gene population was changed at two consecutive time points, and only about 1% genes showed more than a threefold change at any time point studied. Functional Gene Ontology (GO) mapping for both changed and unchanged genes showed similar distribution patterns, except that more genes were changed in the GO clusters of response to stimuli and carbohydrate metabolism. Three distinct expression patterns of genes preferentially expressed in rod photoreceptors were observed in the retina explants. Some genes showed a lag in increased expression, some showed no change, and some continued to have a reduced level of expression. An early downregulation of cyclin D1 in the explanted retina might explain the reduction in numbers of precursors in explanted retina and suggests that external factors are required for maintenance of cyclin D1. The global view of gene profiles presented in this study will help define the molecular changes in retina explants over time and will provide criteria to define future changes that improve this model system.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12177-008-9009-z) contains supplementary material, which is available to authorized users.

Expression of ZnT and ZIP zinc transporters in the human RPE and their regulation by neurotrophic factors

PURPOSE

Zinc is an essential cofactor for normal cell function. Altered expression and function of zinc transporters may contribute to the pathogenesis of neurodegenerative disorders including macular degeneration. The expression and regulation of zinc transporters in the RPE and the toxicity of zinc to these cells were examined.

METHODS

Zinc transporters were identified in a human RPE cell line, ARPE19, using a 28K human array, and their expression was confirmed by PCR, immunocytochemistry, and Western blot analysis in primary human RPE cultures and ARPE19. Zinc toxicity to ARPE19 was determined using monotetrazolium, propidium iodide, and TUNEL assays, and Zn(2+) uptake was visualized with Zinquin ethyl ester. The effect of various growth factors on zinc transporter expression also was examined.

RESULTS

Transcripts for 20 of 23 zinc transporters are expressed in fetal human RPE, 16 of 23 in adult human RPE, and 21 of 23 in ARPE19. Zn transporter proteins were also detected in ARPE19. ZnT5 expression was not observed, whereas ZnT6, ZIP1, and ZIP13 were the most abundantly expressed in all RPE samples. The addition of low concentrations of Zn(2+) to cultures resulted in a dose-dependent increase in intracellular Zn(2+) content in ARPE19, and >30 nM Zn(2+) induced necrosis with an LC(50) of 117.4 nM. Brain-derived neurotrophic factor, ciliary neurotrophic factor, glial-derived neurotrophic factor (GDNF), and pigment epithelial-derived neurotrophic factor (PEDF) increased ZIP2 expression, GDNF and PEDF increased ZnT2 expression, and PEDF increased ZnT3 and ZnT8 expression. These neurotrophic factors also promoted Zn(2+) uptake in the RPE.

CONCLUSIONS

The array of zinc transporters expressed by the RPE may play a key role in zinc homeostasis in the retina and in ocular health and diseases.

A biphasic pattern of gene expression during mouse retina development

BACKGROUND

Between embryonic day 12 and postnatal day 21, six major neuronal and one glia cell type are generated from multipotential progenitors in a characteristic sequence during mouse retina development. We investigated expression patterns of retina transcripts during the major embryonic and postnatal developmental stages to provide a systematic view of normal mouse retina development,

RESULTS

A tissue-specific cDNA microarray was generated using a set of sequence non-redundant EST clones collected from mouse retina. Eleven stages of mouse retina, from embryonic day 12.5 (El2.5) to postnatal day 21 (PN21), were collected for RNA isolation. Non-amplified RNAs were labeled for microarray experiments and three sets of data were analyzed for significance, hierarchical relationships, and functional clustering. Six individual gene expression clusters were identified based on expression patterns of transcripts through retina development. Two developmental phases were clearly divided with postnatal day 5 (PN5) as a separate cluster. Among 4,180 transcripts that changed significantly during development, approximately 2/3 of the genes were expressed at high levels up until PN5 and then declined whereas the other 1/3 of the genes increased expression from PN5 and remained at the higher levels until at least PN21. Less than 1% of the genes observed showed a peak of expression between the two phases. Among the later increased population, only about 40% genes are correlated with rod photoreceptors, indicating that multiple cell types contributed to gene expression in this phase. Within the same functional classes, however, different gene populations were expressed in distinct developmental phases. A correlation coefficient analysis of gene expression during retina development between previous SAGE studies and this study was also carried out.

CONCLUSION

This study provides a complementary genome-wide view of common gene dynamics and a broad molecular classification of mouse retina development. Different genes in the same functional clusters are expressed in the different developmental stages, suggesting that cells might change gene expression profiles from differentiation to maturation stages. We propose that large-scale changes in gene regulation during development are necessary for the final maturation and function of the retina.

Molecular phylogeny of the antiangiogenic and neurotrophic serpin, pigment epithelium derived factor in vertebrates

Background

Pigment epithelium derived factor (PEDF), a member of the serpin family, regulates cell proliferation, promotes survival of neurons, and blocks growth of new blood vessels in mammals. Defining the molecular phylogeny of PEDF by bioinformatic analysis is one approach to understanding the link between its gene structure and its function in these biological processes.

Results

From a comprehensive search of available DNA databases we identified a single PEDF gene in all vertebrate species examined. These included four mammalian and six non-mammalian vertebrate species in which PEDF had not previously been described. A five gene cluster around PEDF was found in an approximate 100 kb region in mammals, birds, and amphibians. In ray-finned fish these genes are scattered over three chromosomes although only one PEDF gene was consistently found. The PEDF gene is absent in invertebrates including Drosophila melanogaster (D. melanogaster), Caenorhabditis elegans (C. elegans), and sea squirt (C. intestinalis). The PEDF gene is transcribed in all vertebrate phyla, suggesting it is biologically active throughout vertebrate evolution. The multiple actions of PEDF are likely conserved in evolution since it has the same gene structure across phyla, although the size of the gene ranges from 48.3 kb in X. tropicalis to 2.9 kb in fugu, with human PEDF at a size of 15.6 kb. A strong similarity in the proximal 200 bp of the PEDF promoter in mammals suggests the existence of a possible regulatory region across phyla. Using a non-synonymous/synonymous substitution rate ratio we show that mammalian and fish PEDFs have similar ratios of <0.13, reflecting a strong purifying selection of PEDF gene. A large number of repetitive transposable elements of the SINE and LINE class were found with random distribution in both the promoter and introns of mammalian PEDF.

Conclusion

The PEDF gene first appears in vertebrates and our studies suggest that the regulation and biological actions of this gene are preserved across vertebrates. This comprehensive analysis of the PEDF gene across phyla provides new information that will aid further characterization of common functional motifs of this serpin in biological processes.

PEDF induces apoptosis in human endothelial cells by activating p38 MAP kinase dependent cleavage of multiple caspases

We examined how pigment epithelium derived factor (PEDF), an effective endogenous antiangiogenic protein, decreases survival of primary cultures of human umbilical vein endothelial cells (HUVECs) in a low serum environment supplemented with the endothelial cell growth factor (VEGF). We provide evidence that induction of apoptosis by PEDF is associated with activation of p38 followed by cleavage of caspases 3, 8, and 9 by treatment with PEDF, and PEDF's actions are caspase dependent. A key mediator in the executioner effects of PEDF is p38 since the inhibition of p38 activity blocked apoptosis and prevented cleavage of caspases 3, 8, and 9. Although PEDF-induced phosphorylation of JNK1, the inhibition of JNK1 had no effect on apoptosis, even though it prevented phosphorylation of JNK1 by PEDF. Based on these findings, we propose that the antiangiogenic action of PEDF is dependent on activation of p38 MAPkinase which regulates cleavage of multiple caspases cascades.

A PEDF N-terminal peptide protects the retina from ischemic injury when delivered in PLGA nanospheres

The neuroprotective effects of small pigment epithelium-derived factor (PEDF) peptides injected intravitreally as free peptides or delivered in poly(lactide-co-glycolide) (PLGA) nanospheres, were tested in retinal ischemic injury. We induced transient ischemia in C57BL/6 mice by elevating the intraocular pressure to the equivalent of 120 mmHg for 60 min, then injected these eyes with one of the following: PBS, full-length native PEDF, N-terminal peptides-PEDF(136-155) and PEDF(82-121), blank PLGA nanospheres or PLGA loaded with PEDF(82-121) (PLGA-PEDF(82-121)). Morphometric analysis and TUNEL assays were used to determine the extent of retinal damage. Transient ischemia caused a rapid reduction in the number of viable cells in the retinal ganglion cell (RGC) layer over 48h as compared to non-ischemic retinas. About 76% surviving cells in the RGC layer were observed in the full-length PEDF protein treated group, whereas only 32% of cells survived in the PBS group. Thus, PEDF prevented approximately 44% of the cell death in the RGC layer resulting from transient ischemia. PEDF(82-121) peptide was as effective as full-length PEDF when injected as either a free peptide or delivered in PLGA nanospheres. PLGA-PEDF(82-121) showed longer-term protection of the RGC layer with no noticeable side effects at 7days. PEDF and PEDF(82-121) lessened damage to the IPL as measured by layer thickness. PEDF and PEDF(82-121) also delayed retinal responses to ischemic injury as measured by GFAP immunolabeling in Müller cells. PEDF(82-121) is an effective neuroprotective peptide in retinal ischemia. PLGA-PEDF(82-121) offers greater protection to the retina suggesting that this peptide and the method of delivering therapeutically active drugs have potential clinical advantages for longer-term treatments of retinal diseases.

PEDF and the serpins: phylogeny, sequence conservation, and functional domains

Pigment epithelium derived factor (PEDF) is non-inhibitory serpin with neurotrophic and antiangiogenic functions. In this study, we have assembled PEDF sequences for 9 additional species by data base mining and performed cross-species alignment for 14 PEDF sequences to identify conserved structural domains. We found evolutionary conservation of a leader sequence, a single C-terminal glycosylation site, collagen-binding residues, and four specific conserved PEDF peptides. The C-terminus, 384--415 and an N-terminal region 78--95, show close homology with many other serpins, and there is strong conservation of 39 of 51 consensus key residues involved in serpin structure and function. Two peptide regions, 40--67 and 277--301, are unique to PEDF but conserved in all species. Conserved residues at the N-terminus, helix d (hD), and helix A (hA) of PEDF form a structure similar to the heparin-binding groove of other serpins. We identified a motif in PEDF that is homologous to the nuclear localization signals of other proteins. A bitopographical localization of PEDF was confirmed by immunocytochemistry and Western blots. Our results suggest that secretion is required for PEDF's activity, that PEDF can migrate to the nucleus, and that PEDF has structural and functional features more common with inhibitory serpins.

STAT3 activation in response to growth factors or cytokines participates in retina precursor proliferation

Growth factors and cytokines play an important role in the development of central nervous systems including neurons of the retina. However, the molecular pathways that trigger cell growth remain unclear in neuronal precursors. In the present studies, we used a retinal explant culture system to investigate the response of signal transducer and activator of transcription factors (STATs) to extrinsic factors during mouse retinal development. Retinas from embryonic and neonatal stages showed that STAT3 but not STAT1 was activated in response to ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), fibroblast growth factor-1 (FGF1), fibroblast growth factor-2 (FGF2), epidermal growth factor (EGF), interferon-alpha (IFN-alpha) and interferon-gamma (IFN-gamma) in distinct patterns. STAT3 activation was detected in the outermost retina layer in response to CNTF, LIF, FGF1, and IFN-alpha 24 hr after stimulation in postnatal day 1 (PN1) explants, but not FGF2, EGF, IFN-gamma, and retinoic acid (RA). Cytokine stimulation increased the number of cells incorporating BrdU and the labelled cells co-localized with phosphorylated STAT3, indicating that STAT3 may play an essential role in coupling extrinsic factors to retina precursor cell (RPC) proliferation. Furthermore, persistent expression of two neural precursor markers, Hes1 and Otx2 was detected in outer retinal layers and correlated with STAT3 activation by CNTF, suggesting that STAT3 activation may play a critical role in stimulating mitotic precursors. These results strongly support a model that STAT3-mediated signalling regulates precursor populations during mouse retina development.

Uncoupling protein-2 is critical for nigral dopamine cell survival in a mouse model of Parkinson's disease

Mitochondrial uncoupling proteins dissociate ATP synthesis from oxygen consumption in mitochondria and suppress free-radical production. We show that genetic manipulation of uncoupling protein-2 (UCP2) directly affects substantia nigra dopamine cell function. Overexpression of UCP2 increases mitochondrial uncoupling, whereas deletion of UCP2 reduces uncoupling in the substantia nigra-ventral tegmental area. Overexpression of UCP2 decreased reactive oxygen species (ROS) production, which was measured using dihydroethidium because it is specifically oxidized to fluorescent ethidium by the superoxide anion, whereas mice lacking UCP2 exhibited increased ROS relative to wild-type controls. Unbiased electron microscopic analysis revealed that the elevation of in situ mitochondrial ROS production in UCP2 knock-out mice was inversely correlated with mitochondria number in dopamine neurons. Lack of UCP2 increased the sensitivity of dopamine neurons to 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine (MPTP), whereas UCP2 overexpression decreased MPTP-induced nigral dopamine cell loss. The present results expose the critical importance of UCP2 in normal nigral dopamine cell metabolism and offer a novel therapeutic target, UCP2, for the prevention/treatment of Parkinson's disease.

Comprehensive in silico functional specification of mouse retina transcripts

BACKGROUND

The retina is a well-defined portion of the central nervous system (CNS) that has been used as a model for CNS development and function studies. The full specification of transcripts in an individual tissue or cell type, like retina, can greatly aid the understanding of the control of cell differentiation and cell function. In this study, we have integrated computational bioinformatics and microarray experimental approaches to classify the tissue specificity and developmental distribution of mouse retina transcripts.

RESULTS

We have classified a set of retina-specific genes using sequence-based screening integrated with computational and retina tissue-specific microarray approaches. 33,737 non-redundant sequences were identified as retina transcript clusters (RTCs) from more than 81,000 mouse retina ESTs. We estimate that about 19,000 to 20,000 genes might express in mouse retina from embryonic to adult stages. 39.1% of the RTCs are not covered by 60,770 RIKEN full-length cDNAs. Through comparison with 2 million mouse ESTs, spectra of neural, retinal, late-generated retinal, and photoreceptor -enriched RTCs have been generated. More than 70% of these RTCs have data from biological experiments confirming their tissue-specific expression pattern. The highest-grade retina-enriched pool covered almost all the known genes encoding proteins involved in photo-transduction.

CONCLUSION

This study provides a comprehensive mouse retina transcript profile for further gene discovery in retina and suggests that tissue-specific transcripts contribute substantially to the whole transcriptome.

Expression of angiogenesis factors in human umbilical vein endothelial cells and their regulation by PEDF

The VEGFs and FGF-2 stimulate angiogenesis. Pigment epithelium-derived factor (PEDF) and thrombospondin-1 (TSP-1) strongly inhibit angiogenesis. Human umbilical vein endothelial cells (HUVECs) expressed VEGF-A, -B, -C, the VEGF receptors R1, R2, and R3, PEDF, FGF-2, and TSP-1, but VEGF-D transcripts were barely detectable. Hypoxia reduced the transcript levels of VEGF-C and its cognate receptor, VEGF-R3. PEDF blocked the effect of CoCl(2) on these two factors. The expression of VEGF-A and -B as well as VEGF-R1 and VEGF-R2 remained unchanged after exposure to hypoxia, PEDF, or both. There was a marked reduction in TSP-1 transcripts in CoCl(2) treated cultures and PEDF blocked this reduction. PEDF induced a small increase in FGF-2 transcripts in HUVECs, but there was no change in FGF-2 expression in HUVECs exposed to hypoxia or hypoxia plus PEDF. PEDF may control neovascularization, in part, by restoring the negative effects of hypoxia on the expression of a potent angiogenesis inhibitor, TSP-1. PEDF may also modulate vascular leakage by maintaining the transcriptional levels of the vascular homeostasis factors, VEGF-C and VEGF-R3 in hypoxic conditions.

Regulation of factors controlling angiogenesis in liver development: a role for PEDF in the formation and maintenance of normal vasculature

PEDF and VEGF are important inhibitors and promoters of angiogenesis, and the ratio between the two is an important indicator in many neovascular diseases. In mouse liver PEDF and VEGF(165) were co-expressed at very early stages of liver development and their expression increased as liver embryogenesis progressed, suggesting that PEDF and VEGF are both crucial to vasculogenesis as well. VEGF(189) only appears at the P0 stage in liver organogenesis and is maintained at high levels thereafter. PEDF and the two VEGF isoforms are synthesized by fresh and cultured hepatocytes. Expression of VEGF(121) and overexpression of VEGF(165) were only seen in HepG2, a well-characterized hepatocellular carcinoma line. The results suggest that hepatic vascular architecture is under the control of both PEDF and VEGF, and that VEGF(165) and VEGF(189) have distinct functions in normal vascular development of the liver. The VEGF isoforms 121 and 189 may be key regulators of increased vascularity and progression of hepatocellular carcinoma, one of the most common malignant tumors, and may be of prognostic significance for this tumor.

Modulation of synaptic function by cGMP and cGMP-gated cation channels

Cyclic nucleotide-gated cation channels have been studied intensively in the primary sensory neurons of the visual and olfactory systems. Using both anatomical and physiological methods we have shown that they have a much more widespread distribution in the nervous system. In many retinal ganglion cells cGMP, but not cAMP, activates a non-selective conductance that has many of the properties of CNG channels. As many neurons also contain cGMP-dependent protein kinases (PKGs), we have used a variety of cGMP analogues to distinguish the actions of cGMP. Sp-8-Br-PET-cGMPS is a potent non-hydrolyzable cGMP analogue that is an agonist of PKG. We found that Sp-8-Br-PET-cGMPS acts as a competitive inhibitor of at least the rod CNG channel. Rp-8-Br-cGMPS has shown the opposite effects, namely as an agonist of the rod CNG channel and an inhibitor of PKG. In dissociated cell cultures and slices of rodent visual cortex cGMP had multiple rapid and reversible effects on transmission at glutamatergic synapses. Extracellular application of 8-Br-cGMP or Sp-8-Br-PET-cGMPS reduced stimulus evoked EPSPs in cortical slices. In cortical cultures both analogs reduced the frequency of spontaneous EPSCs, but not their amplitude. The effects on both EPSPs and EPSCs were presynaptic. The effects on evoked EPSPs may be due, in part, to reduced calcium influx through voltage-gated calcium channels. The effects on spontaneous EPSCs may be due, in part, to modulation of calcium fluxes through internal stores. Similar modulations of synaptic transmission have been found at gabaergic synapses. On postsynaptic cells, PKG activation produced a dramatic enhancement of the responses to applied NMDA. No effects were detected on applied AMPA/kainate or GABA. Together the results suggest that cGMP may use multiple mechanisms to modulate synaptic efficacy and that its actions may include regulating synaptic plasticity and the relative strength of excitatory and inhibitory drive through neural pathways.

Neuroprotective and antiangiogenic actions of PEDF in the eye: molecular targets and therapeutic potential

Pigment epithelium-derived factor (PEDF) is a 50-kDa protein encoded by a single gene that shows strong conservation across phyla from fish to mammals. It is secreted by the retinal pigment epithelium (RPE) and a select number of other cell types in the eye, as well as by other tissues in the body. PEDF was originally defined by its ability to induce differentiation in retinoblastoma cells. It also promotes a non-proliferative, differentiated state in a number of other cell types. PEDF protects retinal neurons from light damage, oxidative stress and glutamate excitotoxicity. PEDF is also antiangiogenic and can inhibit the growth of blood vessels in the eye induced in a variety of ways. A balance in the levels of PEDF and the proangiogenic factor vascular endothelial growth factor-A is perturbed in a range of retinal neovascular diseases. Some of the pathways by which PEDF exerts its actions on cells have now been defined. Peptide fragments of PEDF carry biological activity and may be valuable therapeutic agents that readily penetrate the eye.

STAT3-Mediated Signaling in the Determination of Rod Photoreceptor Cell Fate in Mouse Retina

PURPOSE

The purpose of this study was to determine the intracellular pathways by which ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) negatively regulate the development of rod photoreceptors in the mouse retina.

METHODS

Retina explant cultures derived from timed-pregnant CD-1 mice were used to monitor rod photoreceptor differentiation. CNTF was used to activate the signal transducer and activator of transcription (STAT)-3 and mitogen-activated protein kinase (MAPK) signal transduction pathways. Activation of STAT3 and MAPK were manipulated by using dominant-negative STAT3 recombinant adenoviruses and a specific inhibitor of MAPK, respectively. Explanted retinas were harvested at distinct time points and processed for immunohistochemistry.

RESULTS

Blocking of the MAPK pathway by the MAPK inhibitor PD98059 did not affect normal development of rods in retina explants or the suppression of their appearance by treatment with CNTF. In contrast, activated STAT3 was necessary for suppression of the rod cell fate decision. A deficiency of the STAT3 pathway induced by a dominant negative STAT3 abolished inhibition of rod development by CNTF.

CONCLUSIONS

These results indicate that STAT3, but not MAPK, can critically regulate photoreceptor development during mouse retina development.

Retinoic acid and dexamethasone regulate the expression of PEDF in retinal and endothelial cells

Both all-trans-retinoic acid (ATRA) and pigment epithelial-derived factor (PEDF) regulate cell proliferation and differentiation. Treatment of human Y-79 retinoblastoma and A-RPE 19 pigment epithelial cells with ATRA increased the levels of PEDF protein and RNA. Endothelial cells from bovine retina and human umbilical cord expressed PEDF and the levels were also increased by ATRA. Mouse Müller glial cells and rat C6 glioma cells showed at least a 2.5 fold increase in PEDF RNA levels after ATRA treatment, as measured by quantitative PCR. The PEDF promoter contains a retinoic acid receptor element (RARE). Plasmids containing a PEDF promoter regulating a luciferase gene were transfected into D407 and C6 cells and the luciferase activity measured after incubation in the presence or absence of ATRA. In both cell types ATRA increased the level of luciferase activity suggesting the RARE is functional. Dexamethasone was also effective at increasing PEDF RNA levels in both mouse Muller glial cells and C6 rat glioma cells. To test the effects of PEDF on retinoic acid function, expression of retinoic acid receptors in Y-79 and A-RPE 19 cells was measured by PCR. In Y79 cells, PEDF treatment increased the expression levels of RARalpha and RXRgamma receptors and in the A-RPE 19 cells it resulted in a decrease in expression of the RARbeta and RXRbeta receptors. This study clearly indicates an interaction between PEDF and ATRA. The cell differentiation activities of PEDF may operate through mechanisms orchestrated by retinoids, and the converse may also be true. The differentiation, anti-mitotic, and apoptotic actions of PEDF and ATRA may utilize parallel pathways that converge at key junctional transduction molecules to coordinate cellular quiescence and maintain tissue mass in the presence of signals that stimulate abnormal cell proliferation. It will be an interesting therapeutic strategy to co-administer PEDF and retinoic acid in developing protocols for neovascular diseases in the eye and in cancer.